Studies in the isolated cortical tubule of the rabbit have shown that tubules removed from acidotic rabbits consistently absorb HCO3 in vitro, whereas tubules removed from alkalotic rabbits consistently secrete HCO3. Bladders removed from alkalotic turtles or toads showed enhanced HCO3 for chloride exchange in vitro. The mechanism responsible for adaptive increase in H+ secretion in metabolic or respiratory acidosis is unknown. Ammonia excretion plays an important role in renal acid excretion. The turtle bladder can be utilized to study several aspects of the adaptation to metabolic or respiratory acidosis and ammonia excretion and production, and thus should provide answers to questions not elucidated by previous studies. The specific aims of this proposal are: a. To examine the effect of metabolic or respiratory acidosis in vivo on urinary acidification (H+ secretion and HCO3 secretion) by the turtle bladder in vitro. b. To examine the mechanism(s) whereby metabolic or respiratory acidosis increases H+ secretion by the turtle bladder in vitro by assessing intracellular pH, surface morphology, fluorescence microscopy, and coupling between metabolism and active transport. c. To examine the regulation of ammonia production by the turtle bladder under normal conditions and during metabolic and respiratory acidosis. These studies will provide insight into the mechanisms whereby metabolic or respiratory acidosis increase H+ secretion and ammonia production.